CLAUDE: renderNadirSequence(): dump per-scene sampling grids as -NADIR-SCENE-PXPYD

Save the actual scene-frame pXpYD fed to renderGPUFromDSI (after
transformToScenePxPyD and optional undistort) as a pX/pY/D hyperstack at
tile resolution, one frame per scene, suffix -NADIR-SCENE-PXPYD[-RECTILINEAR].
For offline verification of the nadir render geometry: the grid should be
near-uniform (tile centers + ERS displacement); any residual rotation
proportional to scene roll would explain the halved in-plane rotation
observed in the 2026-07-10 graveyard COLMAP test.
Co-authored-by: Claude <claude@elphel.com>

src/main/java/com/elphel/imagej/tileprocessor/OpticalFlow.java

@@ -10952,6 +10952,9 @@ java.lang.NullPointerException
     	boolean toRGB     = false;
     	String  suffix    = ref_scene.getImageName()
     			+ (undistort ? "-NADIR-MERGED-RECTILINEAR" : "-NADIR-MERGED");
+    	// Debug: collect the actual per-scene sampling grids fed to renderGPUFromDSI
+    	// (scene-frame pXpYD after transformToScenePxPyD and optional undistort).
+    	double[][][] dbg_scene_pXpYD = new double[selected_scenes.length][][];
     	ImageStack stack_scenes = null;
     	for (int nscene = 0; nscene < selected_scenes.length; nscene++) {
     		if (nadir_pXpYD[nscene] == null) continue;
@@ -10981,6 +10984,7 @@ java.lang.NullPointerException
     		if (undistort) {
     			undistortPxPy(pXpYD_scene, selected_scenes[nscene].getErsCorrection());
     		}
+    		dbg_scene_pXpYD[nscene] = pXpYD_scene;
     		// Render from scene's own position: ZERO3 offset, scene is its own reference
     		ImagePlus imp_scene = QuadCLT.renderGPUFromDSI(
     				-1,                               // final int       sensor_mask (-1 = merge all)
@@ -11011,6 +11015,33 @@ java.lang.NullPointerException
     			stack_scenes.addSlice(ts, imp_scene.getStack().getPixels(i));
     		}
     	}
+    	// Save the scene-frame sampling grids as a hyperstack for offline verification
+    	// (same layout as *-NADIR-DISPARITY-MAPS: pX/pY/D per scene at tile resolution)
+    	{
+    		int tilesX = ref_scene.getTilesX();
+    		int tilesY = ref_scene.getTilesY();
+    		String [] slice_titles = {"pX", "pY", "D"};
+    		String [] frame_titles = new String[selected_scenes.length];
+    		for (int ns = 0; ns < selected_scenes.length; ns++) {
+    			frame_titles[ns] = selected_scenes[ns].getImageName();
+    		}
+    		double [][][] disp_maps = ShowDoubleFloatArrays.transposeJagged(
+    				dbg_scene_pXpYD, 3, tilesX * tilesY);
+    		ImagePlus imp_scene_pxpyd = ShowDoubleFloatArrays.showArraysHyperstack(
+    				disp_maps,                                       // double [][][]  pixels,
+    				tilesX,                                          // int            width,
+    				ref_scene.getImageName() + (undistort ?
+    						"-NADIR-SCENE-PXPYD-RECTILINEAR" :
+    						"-NADIR-SCENE-PXPYD"),                   // String         title,
+    				slice_titles,                                    // String []      titles,
+    				frame_titles,                                    // String []      frame_titles,
+    				false);                                          // boolean        show
+    		if (imp_scene_pxpyd != null) {
+    			ref_scene.saveImagePlusInModelDirectory(
+    					null,             // String    suffix,
+    					imp_scene_pxpyd); // ImagePlus imp
+    		}
+    	}
     	if (stack_scenes == null) return null;
     	ImagePlus imp_result = new ImagePlus(suffix, stack_scenes);
     	// Apply unsharp mask to enhance SIFT features in LWIR nadir images